Measurement and remote display of the amount of energy consumed in a household or commercial establishment has been possible for a considerable time.
Several patents show an implementation that utilizes connection or attachment to the utility electrical power meter. Examples of such patents are: U.S. Pat. No. 4,106,095 to Yarbrough, U.S. Pat. No. 4,207,557 to Gilkeson, U.S. Pat. No. 4,233,590 to Gilkeson and U.S. Pat. No. 4,630,211 to Pettis. Other similar devices that are stand alone energy meters require permanent installation in line or at the distribution box. Examples of such patents are: U.S. Pat. No. 4,080,568 to Funk and U.S. Pat. No. 4,182,983 to Heinrich et al. These methods or devices are only able to measure the total energy consumed at the premises and cannot readily provide a measurement of the consumption of a specific load or group of loads within the premises.
It is well known in the art that devices can be made to measure and record the electrical energy used by an appliance. There are a number of patents which reveal portable plug-in devices which can measure the energy consumption by individual appliances, which provides a feed back that can allow the user to modify their electrical usage behaviour in order to conserve electricity or to use electricity at low-demand times. Examples of such patents are: U.S. Pat. No. 4,120,031 to Kincheloe et al, U.S. Pat. No. 4,253,151 to Bouve, and U.S. Pat. No. 4,901,007 to Sworn. These prior art devices are bulky and expensive, frequently requiring considerable expertise in their implementation and use. Furthermore, the configurations of these prior art devices rely upon a connection being made to the receptacle through suitably sized blade terminals. Connection of the appliance under test to the device relies upon a complete receptacle for the connection of the appliance power cord to the device. Energy flow through the device is thus accomplished with suitably large current connecting, contacting and conducting means necessitating large, bulky and expensive devices.
The bulkiness of these prior art devices makes their use problematic as the existing arrangements, since power connection to the appliance must be altered.
Additionally, the current contact conducting and measurement means consume considerable energy in their operation. A common measuring means is the use of a resistor through which all current passes to generate a voltage signal. Even if this resistor is only a few milliohms, more than 1 watt losses are generated at 10 A load levels. These prior art devices were not designed to be used continuously in circuit, so these losses are not substantive in the short term. However, these losses are significant in the long term, rendering such devices unsuitable for continuous use.